As is well known, polyacetal resins have been used in various fields as an engineering plastic due to the excellent physical properties (such as mechanical and electric properties) and chemical properties (such as chemical resistance and heat resistance properties) that such resins possess. However, additional (and more specialized) properties are required of polyacetal resins as new end-use applications are identified. One property of polyacetal resins that is in continual need for improvement is its weather resistance property.
In this regard, polyacetal resins have recently been used to form molded parts for automobile components as well as components for electrical appliances. As can be appreciated, these components are typically exposed to conditions that may disadvantageously affect component properties and/or appearance. For example, automotive components are usually subjected to sunlight, rain and/or outer atmosphere conditions for prolonged time periods. As a result, components used in such end-use environments become discolored and/or lose their surface smoothness or gloss. In addition, cracks may form on the component surfaces thereby disadvantageously affecting the quality of the component. To overcome these problems, weather stabilizers have typically been blended with resins so as to improve the resins' weather resistance properties. However, simply incorporating a weather stabilizer in a polyacetal base resin does not necessarily achieve satisfactory results. Thus, further improvements in the weather resistance properties of polyacetal resins has been needed.
In this connection, a considerable effect can be obtained by incorporating a weather stabilizer and an acrylic resin into a polyacetal base resin. However, the resulting surface conditions (such as crack formation and gloss) and mechanical properties of molded articles formed of such a modified polyacetal resin are not always satisfactory when the articles are exposed to sunlight (ultraviolet rays), rain, and like weather conditions for prolonged time periods. Thus, polyacetal resins having durable weather resistance properties are often required.
Increasing the amounts of the weather stabilizer and the acrylic resin in the overall polyacetal resin compositions results in only limited improvements in the weather resistance properties. Furthermore, an increase in the amount of these additives usually deteriorates the mechanical and physical properties of the resin. In addition, excess weather stabilizer and acrylic resin can cause poor mold release, adhesion to the mold, and mold deposits during molding which can reduce the dimensional accuracy and/or impair the appearance of the molded article, as well as increasing the cleaning frequency of the mold. As a result, the efficiency of the molding operation is reduced.
The present invention broadly relates to polyacetal resin compositions and molded articles formed of the same which retain their "as produced" surface state by inhibiting crack formation when the articles are used outdoors without sacrificing the desirable property characteristics inherent in polyacetal resins generally.
More particularly, the present invention provides a weather-resistant polyacetal resin composition comprising (in weight percentages based on the total weight of the composition):
(A) a polyacetal base resin; PA0 (B) between 0.01 to 5% by weight of a weather stabilizer; PA0 (C) between 1 to 40% by weight of an acrylic resin; and PA0 (D) between 1 to 20% by weight of a fluororesin. PA0 (1) benzotriazoles: PA0 (2) benzophenones: PA0 (3) aromatic benzoates: p-t-butylphenyl salicylate and p-octylphenyl salicylate. PA0 (4) cyanoacrylates: 2-ethylhexyl PA0 (5) oxalanilides: PA0 (6) hindered amines: piperidine derivatives each having a sterically hindered group, such as 4-acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-methocy-2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-phenoxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, 4-(phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-peperidyl) oxalate, bis(2,2,6,6-tetramethyl-4-piperidyl) oxalate, bis(2,2,6,6-tetramethyl-4-piperidyl) malonate, bis(2,2,6,6-tetramethyl-4-piperidyl) adipate, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-pentamethylpiperidyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) terephthalate, 1,2-bis(2,2,6,6-tetramethyl-4-piperidyloxy)ethane, bis(2,2,6,6-tetramethyl-4-piperidyl) hexamehtylene-1,6-dicarbamate, bis(1-methyle-2,2,2,6,6-tetramethyl-4-piperidyl) adipate and tris(2,2,6,6-tetramethyl-4-piperidyl) benzene-1,3,5-tricarboxylate. Furthermore high-molecular piperidine derivative polycondensates such as dimethyl succinate/1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate are also effective.
Further aspects and advantages of the present invention will become more apparent after careful consideration is given to the detailed description of the preferred exemplary embodiment which follows.